Circuit arrangements are often used as multiband frontend modules for mobile telephones. For example, they are connected to the antenna of the mobile telephone at the antenna input. If a user carrying an electrical charge contacts the antenna, this may result in an electrostatic discharge (ESD). Such electrostatic discharges may produce voltage spikes capable of destroying the circuit arrangement. Consequently, it is necessary to equip circuit arrangements of the type mentioned above with a protection device against ESD.
In high-frequency sections of mobile telephones, among other things, components are used that are sensitive to electrostatic discharges. Such components are, for example, surface acoustic wave filters, gallium arsenide switches, PIN diodes, amplifiers or the like. They may be irreversibly destroyed by the action of high-frequency high voltage pulses such as those produced by ESD. These problems are just as relevant to discrete gallium arsenide switches and frontend modules with integrated gallium arsenide switches as they are to frontend modules with pin switching technology and integrated surface wave filters. These problems also concern the ESD-sensitive components that are used in the transmission/reception paths of the high-frequency section. This complicates use in mobile telephones, as a result of which electrostatic discharges directly to the antenna input of the gallium arsenide switch or frontend module are possible in external, accessible antennas, for external antennas on a car. Many manufacturers of mobile telephones therefore require that the frontend modules or gallium arsenide switches have ESD resistance in compliance with standard IEC61000-4-2 in the magnitude of 8 kV at the system level.
Circuit arrangements that are equipped with a protection device against ESD are known from the publication WO 00/57515. The protection device is designed as an electric high pass filter, to which a capacitor is connected in series with the antenna input path and an inductance is connected in parallel.
The high pass filter to protect the circuit arrangement has the disadvantage that the function of the protective element is frequency-dependent. All frequency components of a signal are passed through nearly unhindered from a specific limit frequency. All other frequency components are suppressed. The result of this frequency-dependent operating mode is that very many frequencies that are not desired in a mobile telephone are still allowed through. For example, frequencies between approximately 1 and 2 GHz are used in mobile telephones according to the GSM, PCN or PCS standard. All other frequencies received by the antenna are likely to be interfering and must therefore be filtered out.